**SOLVED** - the answer is 2 weeks of evenings, a lot of hair lot, but a feeling of achievement!
My needs are incredibly simple:
Caller dials in. Selects from 2 options:
1: Listen to tracks.
2: Listen to contact info and leave feedback in a voicemail.
And under menu 1:
Between 1 and 9 tracks, plus zero to go back to selection.
Tracks play one after another.
There is transport control on the tracks (pause, skip etc).
So easy, that I had Asterisk installed, running and doing just that on Ubuntu in under an hour just playing with the hard coded conf files and one incoming SIP number.
Let's say I now want to add more lines, easily. Add a number, directory and structure to hold the tracks. And add two more features - simple PIN access to the tracks on some numbers (should be optional), and if the incoming caller hangs up halfway through a track, then recognise the CLI if they redial within 24 hours and ask if they want to continue from that point.
There is to be NO other PBX functionality.
Probably less than an hour for someone who knows what they are doing, but this will be used by charities, so before I know where I'm going with this, can someone give me a rough guide price for what this kind of thing should come in at? I'll be providing the server, you just need to show me the config files basically, and I can do the rest!